asymmetry bidirectional relationship

I want to add a relationship pair in my site - teacher and student.
I add two relationships - teacher and student, and make them imply each other.(skip the bug I mentioned in another issue)

But I find that it doesn't work the way as I wish.
When I (user A) add a user B as my student, I receive a teacher relationship request from B which is generated by module automatically. After I approve the teacher request, I become a teacher of user B.
But it doesn't make sense because user B hasn't approve my student relationship request yet. How can I be a teacher of him?

So I suggest a asymmetry bidirectional relationship.
I can add user B as my student and I become his teacher if and only if my request is approved.
In the other side, I can add user B as my teacher and I become his student if and only if my request is approved.